Substrate with contact array and substrate assemblies

ABSTRACT

A substrate assembly including a substrate and a plurality of spring-biased electrical contacts formed thereon for establishing electrical contact with the lead elements of an IC device. The substrate assembly also comprises a layer of resilient conductive material formed on a surface of the substrate, the spring-biased electrical contacts being formed in the resilient conductive material layer in situ on the substrate. Each spring-biased electrical contact includes a surface or surfaces configured to bias against and electrically contact an IC device lead element. The present invention also encompasses methods of fabricating substrate assemblies according to the invention, including heat treating the substrate assembly after formation to achieve desired spring characteristics.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the assembly andtesting of integrated circuit device components, such as multichipmodules. Specifically, the present invention relates to a device andmethod for removably securing an integrated circuit device to asubstrate and, in particular, to an array of spring-biased electricalcontacts formed in a layer of resilient conductive material on asubstrate and configured for establishing nonpermanent electricalconnections between the lead elements of an integrated circuit deviceand the substrate.

[0003] 2. State of the Art

[0004] Integrated circuit (IC) devices, such as Ball Grid Array (BGA)packages, Small Outline J-Lead (SOJ) packages, and Thin Small OutlinePackages (TSOPs) are commonly assembled into multichip modules forconnection to higher-level packaging, such as a motherboard or apersonal computer chassis. Generally, a multichip module (MCM) includesa carrier substrate, such as a printed circuit board, having a pluralityof IC devices mounted thereto. Other electrical components, such asresistors, capacitors, inductors, or other suitable devices, may also bemounted on the carrier substrate of the MCM or even on the IC devices.Electrical communication among the IC devices, between the IC devicesand other electrical components on the multichip module, and between thedevices and external components is established by conductors on the MCMcarrier substrate. The conductors may be conductive traces fabricated onthe surface of, or internal to, a printed circuit board. Methods forfabricating printed circuit boards having conductive traces, as well asother types of substrates having conductors thereon, are well-known inthe art.

[0005] Conventional IC devices, such as BGA packages, SOJ packages, andTSOPs, generally comprise a semiconductor die electrically connected toa plurality of electrical leads that are encased within an encapsulantmaterial, a portion of each of the electrical leads extending from theencapsulant material and configured for establishing electricalconnections between the semiconductor die and external components orhigher level packaging. By way of example, an exemplary embodiment of aconventional BGA package is shown in FIGS. 1 and 2. The conventional BGApackage 10 includes a semiconductor die 20 secured to a die-attach pad35 formed on an upper surface 31 of a substrate 30, which may also betermed an interposer. The BGA package 10 also includes a plurality ofelectrical leads 40 adapted to provide electrical communication betweenthe semiconductor die 20 and one or more external components (notshown). The semiconductor die 20 and at least a portion of eachelectrical lead 40 may be encased by an encapsulant material 50. Theconventional BGA package 10 may be a memory device, such as a DRAM chip,a processor, or any other integrated circuit device known in the art.

[0006] Each of the electrical leads 40 includes an external conductiveball (or bump, pillar, or other lead element) 41 configured forelectrical connection to an external component. The conductive ball 41may be secured to a conductive pad 42 formed on a lower surface 32 ofthe substrate 30. Each electrical lead 40 further comprises a conductivevia 43 extending from the conductive pad 42 and through the substrate 30to a conductive trace 44. The conductive trace 44 (only a few of whichare shown in FIG. 1 for clarity) is formed on the upper surface 31 ofthe substrate 30 and provides an electrical path from the conductive via43 to a bond end 45 located proximate the semiconductor die 20. A bondwire 46 attached to the bond end 45 of the conductive trace 44 andextending to the semiconductor die 20, where the bond wire 46 isattached to a bond pad thereon, electrically connects the electricallead 40 to the semiconductor die 20. At least the bond wire 46 and theconductive trace 44 of each electrical lead 40 may be encased by theencapsulant material 50.

[0007] The conventional BGA package 10 may include a plurality of theconductive balls 41 arranged, for example, in an array or arrays ofmutually adjacent rows and columns. Referring to FIG. 1, the conductiveballs 41 may be arranged in two arrays 60, 70, each array 60, 70disposed between an edge of the semiconductor die 20 and a peripheraledge of the substrate 30. Each array 60, 70 comprises three columns 61,62, 63, 71, 72, 73, respectively, of conductive balls 41. Thearrangement of conductive balls 41 is typically referred to as the“pin-out” or the “footprint” of the BGA package 10. Those of ordinaryskill in the art will understand that the particular pin-out of the BGApackage 10 may vary depending upon the application and that the pin-outmay be of any suitable configuration.

[0008] To attach and electrically connect the conductive balls 41 of theBGA package 10 to a substrate—such as, for example, an MCM carriersubstrate or a burn-in board—the substrate is configured with aplurality of contact pads arranged in a number of contact pad arrays.Each contact pad array includes a number of contact pads arranged in apattern corresponding to the pinout of the BGA package 10. Theconductive balls 41 of the BGA package 10 may be formed of solder or aconductive or conductor-filled epoxy. If solder, the conductive balls 41are reflowed to connect to the contact pads of the contact pad array onthe substrate. If epoxy, the conductive balls 41 may be first heated toa tacky “B” stage to adhere to the contact pads, and then further heatedto completely cure the epoxy to a “C” stage. A substrate may include aplurality of IC devices mounted thereto, wherein each of the IC devicesis permanently attached to a corresponding contact pad array on asurface of the substrate. By way of example, an MCM may be a memorymodule comprised of a carrier substrate having opposing surfaces, withone or both of the opposing surfaces of the carrier substrate includingmultiple contact pad arrays and a plurality of IC devices, such as BGApackages, SOJ packages, and/or TSOPs, mounted thereto.

[0009] During the fabrication of an IC device, the IC device may besubjected to individual component-level testing, such as burn-in andelectrical testing. An IC device that exhibits a desired level ofperformance during component level testing is generally referred to as a“known good device” or “known good die” while an IC device failing tomeet minimum performance characteristics may be referred to as a “knownbad device.” After component-level testing, the IC device may beassembled into higher level packaging, such as an MCM, and againsubjected to testing. Testing of higher level packaging such as anMCM—referred to herein as module level testing—may include burn-in,electrical characterization and performance evaluation, as well as otherdesired electrical testing.

[0010] If an MCM fails to exhibit minimum operating characteristicsduring module level testing, an IC device causing the failure—which mayhave previously been identified as a “known good device” duringcomponent level testing—must be removed from the MCM and replaced. Also,it may be desirable to introduce a “known bad” IC device into an MCM formodule level testing in order to observe the electrical characteristicsof the MCM with the “known bad” IC device, or to observe the electricalcharacteristics of the “known bad” IC device at the module level. Aftermodule level testing is complete, the “known bad” IC device must beremoved from the MCM and replaced. Thus, although individual IC devicesare typically tested at the component level, it is desirable to subjectIC devices to further testing at the module level, as a “known gooddevice” may fail at the module level and, further, because incorporationof a “known bad device” into an MCM may be useful in module leveltesting.

[0011] To test IC devices in a higher level environment, module leveltesting is generally performed after the IC devices are assembled intoand permanently attached to, for example, an MCM carrier substrate.Thus, if an IC device must be removed from an MCM after module leveltesting, the permanent electrical bonds between the electrical leads ofthe IC device—for example, the conductive balls 41 of the conventionalBGA package 10—and the contact pads on the MCM carrier substrate must besevered. Severing the permanent electrical bonds—which typicallycomprise solder or conductive epoxy—may cause both heat-induced andmechanical damage to the MCM carrier substrate and conductors, to theelectrical leads and electrical bonds of the IC devices remaining on theMCM, and to other electrical components mounted on the MCM.

[0012] Also, it may be necessary to remove an IC device from a substrateto achieve an upgrade. For example, as technological advances are madeby IC device manufacturers, it is often desirable to replace an ICdevice mounted to a substrate with a next-generation IC deviceexhibiting improved performance characteristics. To replace an obsoleteIC device mounted to a substrate—such as the carrier substrate of an MCMcomprising part of, for example, a personal computer—the permanentelectrical bonds between the electrical leads of the obsolete IC deviceand a plurality of contact pads on the substrate must be severed, whichmay cause both heat-induced and mechanical damage to the substrate andto other IC devices remaining on the substrate.

[0013] To prevent heat-induced and mechanical damage resulting fromsevering of the permanent electrical bonds between the electrical leadsof an IC device and a plurality of contact pads on a substrate, the ICdevice may be nonpermanently attached to the substrate for module leveltesting, as well as for final assembly. Use of nonpermanent connectionsbetween the electrical leads of an IC device and a contact pad array ofa substrate allows for easy removal of the IC device after module leveltesting or after final assembly without any resulting damage from thesevering of permanent electrical bonds. Sockets and fixtures fornonpermanently attaching an IC device to a substrate are well-known inthe art; however, such sockets can be relatively expensive and theircost often does not justify their use. Although the cost of conventionalsockets and fixtures may, in some instances, be acceptable for limiteduse applications, such as testing and small production runs, their costis generally not acceptable for full scale production.

[0014] Use of nonpermanent electrical connections between the electricalleads of an IC device and a contact pad array of a substrate can,however, itself cause problems during module level testing and/or atfinal assembly. Non-planarities in the substrate, in the conductorsforming a contact pad array, or in the IC device itself, may—in theabsence of a permanent bonding agent—result in poor electrical contactbetween an electrical lead of the IC device and a corresponding contactpad on the substrate. For example, nonplanarities in the substrate 30 ofthe BGA package 10, as well as inconsistency in size of the conductiveballs 41, may result in unreliable electrical contact between theconductive balls 41 and the contact pads of a substrate in the absenceof a permanent bonding agent. Similarly, for other types of IC devices,such as the SOJ package or the TSOP, deflection of their electricalleads as they come into contact with the contact pads on the substratemay—again, in the absence of a permanent bonding agent such as solder orconductive epoxy—result in poor electrical contact. Poor electricalcontact resulting from nonplanarities and/or lead deflections mayproduce unreliable test data during module level testing or prohibit theacquisition of any meaningful test data and such poor electrical contactmay result in nonfunctional, assembled IC device components.

[0015] Therefore, a need exists in the art for a low-cost device andmethod of forming nonpermanent, reliable electrical connections betweenthe electrical leads of an IC device and a contact pad array of asubstrate. Such an apparatus and method must also provide for robust,compliant and reliable electrical connections between the electricalleads of an IC device and the contact pads on a substrate.

SUMMARY OF THE INVENTION

[0016] The present invention comprises embodiments of a substrateassembly including a plurality of spring-biased electrical contacts forestablishing electrical contact with the lead elements extending from anIC device. The substrate assembly comprises a substrate having an uppersurface and an opposing lower surface, and the substrate assemblyfurther comprises a layer of resilient conductive material disposedproximate at least one of the upper and lower surfaces of the substrate.The layer of resilient conductive material comprises any suitableconductive material that also exhibits elastic properties suitable forthe formation of the spring-biased electrical contacts and, further, theresilient conductive material layer may be formed on the substrate usingany suitable deposition process or may be a separately formed laminatebonded to a surface of the substrate.

[0017] A plurality of electrically isolated conductive traces are formedin the layer of conductive material. At least some of the conductivetraces each terminate at a spring-biased electrical contact also formedin the resilient conductive material layer. Each spring-biasedelectrical contact is electrically isolated from the layer of resilientconductive material layer by an aperture formed in the resilientconductive material layer.

[0018] A spring-biased electrical contact includes a surface or surfacesconfigured to bias against and establish both physical and electricalcontact with a lead element of an IC device, and the spring-biasedelectrical contact may also be configured to align the IC device leadelement relative thereto. The spring-biased electrical contact may beconfigured as, for example, a cantilevered spring, a transverselydeflecting hoop-shaped spring, a spiral-shaped spring, or a rosettespring. A via formed in the substrate and opening onto at least one ofits surfaces may underlie a spring-biased electrical contact, providinga recess into which the spring-biased electrical contact can deflectupon engagement with an IC device lead element. Also, a spring-biasedelectrical contact may be preformed with a permanent deflection towardsor away from the underlying substrate surface, in which case a subjacentvia may be eliminated. A spring-biased electrical contact may furtherinclude one or more contact elements configured to wipe away or puncturethrough oxides and other contaminants on the exterior surface of an ICdevice lead element. Further, the substrate assembly may include a layerof dielectric material overlying the layer of resilient conductivematerial and having apertures therethrough substantially aligned withthe spring-biased electrical contacts. The overlying dielectric layermay be of sufficient thickness so that the apertures therethrough assistwith alignment of conductive balls or bumps of an IC device to bemounted to the substrate assembly in a flip chip configuration.

[0019] A plurality of IC devices may be mounted to a substrate assemblyaccording to the invention to form a multichip module. The IC devicesmay be mounted to either one or both of the surfaces of a substrate ofthe substrate assembly. The substrate may include a plurality ofspring-biased electrical contacts arranged in one or moretwo-dimensional arrays, each array corresponding to the pinout of an ICdevice to be mounted thereon. A clamping element may be used to securean IC device to the substrate and to bias the lead elements of the ICdevice against the spring-biased electrical contacts.

[0020] The present invention also encompasses methods of manufacturing asubstrate assembly according to the invention. One embodiment of such amethod includes the acts of providing a substrate, forming a layer ofresilient conductive material on a surface of the substrate, followed byforming conductive traces, spring-biased electrical contacts, andapertures in the resilient conductive material layer and furtherincluding heat treating the substrate assembly. Subjecting the substrateassembly to a heat treatment after formation enables the realization ofdesired mechanical properties for the spring-biased electrical contactswhile also providing for suitable mechanical properties in the resilientconductive material layer during formation of the conductive traces,spring-biased electrical contacts, and apertures.

[0021] In another embodiment of a method of manufacturing a substrateassembly according to the invention, the method further includes the actof forming vias in the substrate. A further embodiment of a method ofmanufacturing a substrate assembly according to the invention comprisesthe additional act of preforming one or more of the spring-biasedelectrical contacts. Yet another embodiment of a method of manufacturinga substrate assembly according to the invention includes the act offorming contact elements on one or more of the spring-biased electricalcontacts.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0022] While the specification concludes with claims particularlypointing out and distinctly claiming that which is regarded as thepresent invention, the features and advantages of this invention can bemore readily ascertained from the following detailed description of theinvention when read in conjunction with the accompanying drawings, inwhich:

[0023]FIG. 1 shows a plan view of an exemplary embodiment of aconventional BGA package;

[0024]FIG. 2 shows a cross-sectional view of the conventional BGApackage as taken along line II-II of FIG. 1;

[0025]FIG. 3 shows a plan view of a substrate assembly according to thepresent invention;

[0026]FIG. 4 shows a cross-sectional view of the substrate assemblyaccording to the invention as taken along line IV-IV of FIG. 3;

[0027]FIG. 4A shows a typical tool used to form the spring-biasedelectrical contacts on the substrate assembly;

[0028]FIG. 5 shows a cross-sectional view of the substrate assemblyaccording to the invention as taken along line IV-IV of FIG. 3 andfurther including a conventional BGA package as shown in FIGS. 1 and 2;

[0029]FIG. 6 shows a cross-sectional view of a portion of the substrateassembly of FIGS. 3 through 5, including an embodiment of aspring-biased electrical contact;

[0030]FIG. 7 shows a cross-sectional view of a portion of the substrateassembly of FIGS. 3 through 5, including an alternative embodiment of aspring-biased electrical contact;

[0031]FIG. 8 shows a cross-sectional view of a portion of the substrateassembly of FIGS. 3 through 5, including another alternative embodimentof a spring-biased electrical contact;

[0032]FIG. 9 shows a cross-sectional view of a portion of the substrateassembly of FIGS. 3 through 5, including a further alternativeembodiment of a spring-biased electrical contact;

[0033]FIG. 10 shows a plan view of a substrate and a spring-biasedelectrical contact according to yet another alternative embodiment ofthe invention;

[0034]FIG. 11 shows a cross-sectional view of the substrate andspring-biased electrical contact as taken along line XI-XI of FIG. 10;

[0035]FIG. 12 shows a plan view of a substrate and a spring-biasedelectrical contact according to yet a further alternative embodiment ofthe invention;

[0036]FIG. 13 shows a cross-sectional view of the substrate andspring-biased electrical contact as taken along line XIII-XIII of FIG.12;

[0037]FIG. 14 shows a plan view of a substrate and a spring-biasedelectrical contact according to another alternative embodiment of theinvention;

[0038]FIG. 15 shows a cross-sectional view of the substrate andspring-biased electrical contact as taken along line XV-XV of FIG. 14;

[0039]FIG. 16 shows a cross-sectional view of a multichip moduleincorporating a substrate and a plurality of spring-biased electricalcontacts according to the invention; and

[0040]FIG. 17 shows a flow chart summarizing various embodiments ofmethods of fabricating a substrate assembly according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Shown in FIGS. 3 through 6 is an embodiment of a substrate and aplurality of electrical contacts according to the present invention forestablishing electrical contact with the lead elements of an IC device,such as the conventional BGA package 10 shown in FIGS. 1 and 2. Theembodiments of a substrate and electrical contacts, or substrateassembly, of the present invention are described herein in the contextof mounting and establishing electrical connections with a BGA package10; however, those of ordinary skill in the art will understand that thesubstrate assembly of the instant invention may be used with other typesof IC devices, such as, for example, an SOJ package or a TSOP. As usedherein, the term “lead element” refers to and encompasses any typeconductive ball, pillar, or bump extending from an IC device, as well asa lead finger extending from an IC device having leadframe construction,such as, for example, a TSOP or SOJ package.

[0042] Referring to FIGS. 3, 4, and 6, a substrate assembly 100comprises a substrate 120 including an upper surface 122 and an opposinglower surface 124. The substrate 120 may comprise an MCM carriersubstrate and, further, may be constructed of a printed circuit board(PCB) material, such as FR-4, according to conventional, well-known PCBfabrication techniques. However, the substrate 120 may be adapted toother, alternative applications, such as a burn-in board or other testboard. Also, the substrate 120 may be constructed of any other suitabledielectric or nonconducting materials known in the art, includingplastics, resins, composites, glasses, ceramics, and other oxidematerials. Those of ordinary skill in the art will appreciate that thelabels “upper” surface 122 and “lower” surface 124 are arbitrary andthat either of the surface 122, 124 of the substrate 120 may be referredto as the upper surface. Further, the substrate surfaces 122, 124 mayalternatively be referred to as simply the first and second surfaces.

[0043] The substrate assembly 100 further comprises a layer of resilientconductive material 130 formed on at least the upper surface 122 of thesubstrate 120 or a suitable portion thereof 122. The layer of resilientconductive material 130 comprises any suitable conductive material thatalso exhibits elastic properties suitable for the formation ofspring-biased electrical contacts, as will be described in greaterdetail below. By way of example, the layer of resilient conductivematerial 130 may comprise a copper alloy material, such as berylliumcopper. The layer of resilient conductive material 130 may be formed onthe substrate 120 using any suitable process. For example, the layer ofresilient conductive material 130 may be formed on the upper surface 122of the substrate 120 using a sputtering process, a chemical vapordeposition (CVD) process, or any other suitable deposition process knownin the art. Alternatively, the layer of resilient conductive material130 may be a separately formed laminate that is subsequently secured to,or laminated on, the upper surface 122 of the substrate 120 using, forexample, an adhesive and/or a thermocompression bonding process.

[0044] Referring to FIGS. 3 and 4, the layer of resilient conductivematerial 130 includes a plurality of conductive traces 132 formedtherein, at least some of the conductive traces 132 each terminating ata spring-biased electrical contact 160. Each conductive trace 132 isformed by removing a portion of the layer of resilient conductivematerial 130 to form cavities 133, which cavities 133 define theconductive trace 132 and electrically isolate the conductive trace 132from all other conductive traces 132 (as well as from otherspring-biased electrical contacts 160) formed on the substrate 120. Thecavities 133 extend through the layer of resilient conductive material130 at least to the upper surface 122 of the substrate 120, and thecavities 133 may extend a depth into the substrate 120. Any suitableprocess known in the art, such as chemical etching or laser ablation,may be used to form the conductive traces 132 and cavities 133.

[0045] As noted above, at least some of the conductive traces 132 eachterminate at a spring-biased electrical contact 160. Referring to FIGS.3 through 6, each spring-biased electrical contact 160 comprises, forexample, a cantilevered spring 162 formed in the layer of resilientconductive material 130 and configured to bias against and formelectrical contact with a conductive ball 41 of the BGA package 10 orother lead element. The cantilevered spring 162 includes an uppersurface 164 for making physical and electrical contact with theconductive ball 41 (shown in dashed line in FIGS. 3, 4, and 6). Anaperture 136 formed in the resilient conductive layer 130 around thecantilevered spring 162 separates and electrically isolates thecantilevered spring 162 from the remainder of the layer of resilientconductive material 130. The spring-biased electrical contacts 160 andsurrounding apertures 136 may also be formed using a chemical etching orlaser ablation process, and the shapes of the spring-biased electricalcontacts 160 and apertures 136 may also be cut or formed using astamping process.

[0046] It should be noted that the layer of resilient conductivematerial 130 may be sandwiched between a lower dielectric layer ofsubstrate 120 and an upper dielectric layer thereof which overlies layerof resilient conductive material 130, upper dielectric layer definingupper surface 124. Referring to FIGS. 4 and 5 of the drawings, anexemplary overlying dielectric or insulative layer 121 having apertures123 therein substantially aligned with apertures 136 may be disposedover the layer of resilient conductive material 130 after formation ofthe conductive traces 132 and spring-biased electrical contacts 160. Theapertures in overlying dielectric layer 121 may be sized and configuredto receive portions of conductive balls 41 of a BGA package (see FIG. 5and description below) therein, and overlying dielectric layer may be ofsufficient thickness to assist with alignment of conductive balls 41with spring-biased electrical contacts 160. If desired, apertures 123may be of frustoconical shape as shown at broken lines 123′ with a widerupper portion to assist in the initial alignment of conductive balls 41.

[0047] Referring to FIG. 4A, a cutting tool 160′ is illustrated that isused to form the spring-biased electrical contacts 160. The cutting tool160′ comprises a generally cylindrical body or shaft portion 702terminating in a substantially flat end 708 substantially located in aplane 710 which is located with respect to a vertical axis, such as 712,the body or shaft portion 702 having a helical cutting spiral 704attached to and/or formed thereon. The helical cutting spiral 704terminates in a cutting face 706 located at the bottom end of the spiral706 in substantially the same plane 710 as the end 708 of the body orshaft portion 702. The helical cutting spiral 704 may be formed at anysuitable helical angle on the body or shaft portion 702 depending uponthe amount of desired rotation of the cutting tool 160′ is to be used toform a spring-biased electrical contact 160. If desired, the end 708 ofthe cutting tool 160′ may protrude beyond plane 710 in any suitableshape (illustrated in a dashed line 714) to be used as a pilot whenengaged in aperture 126 of substrate 120 for the forming of thespring-biased electrical contact 160. The cutting face 706 of thehelical cutting spiral 704 may be any suitable shape capable of formingthe desired shape of the spring-biased electrical contact 160. Forexample, the cutting face 706 may be concave shaped, convex shaped, acombination of concave and convex shaped, etc. To form the spring-biasedelectrical contact 160, the cutting tool 160′ is placed upon on theprecursor structure of the spring-biased electrical contact 160, such asillustrated in FIG. 3 when the precursor structure of spring-biasedelectrical contact 160 is a layer on the substrate 120, and the cuttingtool 160′ subsequently rotated a desired amount for cutting face 706 tocut through a portion or the entirety of the precursor structure (layer)to form a length of resilient material and cause a portion thereof to bebent upwardly along the helical cutting spiral 704. Thereafter, thecutting tool 160′ is rotated in the opposite direction to remove thecutting tool 160′ from the formed spring-biased electrical contact 160.

[0048] The substrate 120 may include a via 126 formed therethroughsubstantially concentric with each aperture 136 formed in the resilientconductive layer 130. A via 126 extending through the substrate 120provides a recess into which a corresponding spring-biased electricalcontact 160, such as cantilevered spring 162, can deflect upon contactwith a conductive ball 41 of the BGA package 10. The via 126 may alsoprovide a port through which a tool may be inserted to push outwardly onthe cantilevered spring 162 to permanently deflect the cantileveredspring 162 away from the upper surface 122 of the substrate 120 (seeFIG. 6). Permanently deflecting, or preforming, the cantilevered spring162, such that the cantilevered spring 162 is initially deflected awayfrom the substrate 120 in an unbiased state, can increase the totaldeflection of the cantilevered spring 162 upon contact with a conductiveball 41, thereby increasing the force exerted by the cantilevered spring162 against the conductive ball 41 and improving the electrical contacttherebetween.

[0049] Referring to FIGS. 3, 4, and 5, the substrate 120 may include aplurality of spring-biased electrical contacts 160 arranged in atwo-dimensional array 161 corresponding to the pin-out of the BGApackage 10, the vias 126 extending through the substrate 120 also beingarranged in a two-dimensional array corresponding to the pin-out of theBGA package 10. With reference to FIG. 5, a BGA package 10 having aplurality of conductive balls 41 may then be nonpermanently mounted tothe substrate assembly 100, the two-dimensional array 161 ofspring-biased electrical contacts 160 on substrate 120 establishingnonpermanent electrical connections with the conductive balls 41,respectively, of the BGA package 10. Thus, each conductive ball 41 ofthe BGA package 10 is engaged with and in electrical contact with acorresponding spring-biased electrical contact 160—such as acantilevered spring 162—formed on the upper surface 122 of the substrate120.

[0050] A clamping element 90 may be used to secure the BGA package 10 tothe substrate 120 and to bias the conductive balls 41 thereof againstthe spring-biased electrical contacts 160 formed in the resilientconductive layer 130. The clamping element 90 may be any suitable clipor clamp known in the art adapted to secure the BGA package 10 to thesubstrate 120. For example, the clamping element 90 may comprise astab-in-place clip 95 having one or more resilient tabs or prongs 96configured for insertion into corresponding holes 128 in the substrate120. The resilient tab or tabs 96 are retained by the mating hole orholes 128 to secure the BGA package 10 to the substrate 120 and to biasthe conductive balls 41 thereof against the spring-biased electricalcontacts 160. Typically, such stab-in-place type clips are injectionmolded from plastic materials and are relatively inexpensive. Inaddition to the foregoing, it is also contemplated that variousapparatus disclosed and claimed in copending U.S. patent applicationSer. No. 09/478,619, filed Jan. 5, 2000 and assigned to the assignee ofthe present invention may be employed to secure BGA package 10 to thesubstrate 120. The disclosure of U.S. patent application Ser. No.09/478,619 is hereby incorporated herein by reference.

[0051] In an alternative embodiment, as shown in FIG. 7, a spring-biasedelectrical contact 160 comprises a cantilevered spring 162 that is notpermanently deflected outwardly away from the upper surface 122 of thesubstrate 120 but, rather, that is preformed with a permanent deflectioninto its mating via 126 in the substrate 120. Use of such an inwardlydeflected cantilevered spring 162 may facilitate alignment with a matingconductive ball 41 (shown in dashed line in FIG. 7) of the BGA package10. Specifically, the inwardly deflected cantilevered spring 162functions to guide the conductive ball 41 toward the wall 127 of the via126, thereby essentially pinching the conductive ball 41 between thecantilevered spring 162 and the wall 127 of the via 126. In a furtherembodiment, although not shown in the figures, a spring-biasedelectrical contact 160 may comprise a generally planar cantileveredspring 162 that has no permanent deflection and that is essentiallyparallel with the upper surface 122 of the substrate 120.

[0052] In another alternative embodiment, as shown in FIG. 8, thecantilevered spring 162 is suspended over a via 126 that opens only tothe upper surface 122 of the substrate 120. The via 126 extends into thesubstrate 120 a depth sufficient only to provide a relief into which thecantilevered spring 162—or the spring-biased electrical contact 160generally—can deflect upon contact with a conductive ball 41 (shown indashed line in FIG. 8) of the BGA device 10. In a further alternativeembodiment, as shown in FIG. 9, the cantilevered spring 162—or thespring-biased electrical contact 160—generally is positioned directlyover the upper surface 122 of the substrate 120 and no corresponding viais provided subjacent the cantilevered spring 162. In the embodiment ofFIG. 9, the cantilevered spring 162 is preformed with a permanentdeflection outwardly away from the upper surface 122 of the substrate120, such that the cantilevered spring 162 can deflect downward uponengagement with a conductive ball 41 (shown in dashed line if FIG. 9) ofthe BGA package 10.

[0053] In another embodiment of the present invention, the spring-biasedelectrical contact 160 includes one or more contact elements configuredto wipe away and/or puncture through a layer of oxide and/or othercontaminants formed on an exterior surface of a conductive ball 41. Forexample, referring to FIG. 6, the cantilevered spring 162 includes aplurality of grooves 191 formed into the upper surface 164 thereof andseparated by ridges 192. Impingement of the ridges 192 of thecantilevered spring 162 against the outer surface of a conductive ball41, in conjunction with relative motion therebetween, will cause theridges to wipe or scrape against the exterior surface of the conductiveball 41 and to remove oxides and other contaminants therefrom. Thegrooves 191 and ridges 192 may be formed on a spring-biased electricalcontact 160 using any suitable cleaving or cutting process, and thegrooves 191 and ridges 192 may also be formed using a stamping process.

[0054] Alternatively, contact elements may comprise one or more barbs orprotrusions formed on a spring-biased electrical contact 160 andextending therefrom. For example, referring to FIG. 8, a cantileveredspring 162 may include a plurality of barbs or protrusions 193 formed onan upper surface 164 thereof and extending generally upwards away fromthe upper surface 164. The barbs or protrusions 193 can impinge againstand puncture through layers of oxide and other contaminants on theexterior surface of a conductive ball 41 to form electrical contacttherewith. The barbs or protrusions 193 may be formed using any suitabledeposition process, as noted above. Alternatively, a barb or protrusion193 may be formed by puncturing a hole through, for example, acantilevered spring 162 and subsequently pushing (or pulling) a portionof the cantilevered spring 162 around the periphery of the hole upwardlyto form a barb or protrusion 193.

[0055] Also, a contact element may simply comprise a roughened surfaceformed on a spring-biased electrical contact 160. Referring to FIG. 9, acantilevered spring 162 has an upper surface 164 including at least aroughened portion 194. The roughened portion 194 of the upper surface164 can impinge against and move over the exterior surface of aconductive ball 41 to remove (by a scraping or wiping action) oxides andother contaminants therefrom.

[0056] A spring-biased electrical contact 160 may comprise alternativeshapes or configurations other than the cantilevered spring 162 shownand described with respect to FIGS. 3 through 9. For example, withreference to FIGS. 10 and 11, a spring-biased electrical contact 160 maycomprise a transversely deflecting, hoop-shaped spring 262 formed in thelayer of resilient conductive material 130. The hoop-shaped spring 262comprises two semicircular arms 263 a, 263 b formed within an aperture136 in the resilient conductive layer 130 and suspended over a via 126formed in the substrate 120, the respective ends of the semicirculararms 263 a, 263 b being separated by a gap 264. The semicircular arms263 a, 263 b are configured—upon engagement with a conductive ball 41(shown in dashed line in FIGS. 10 and 11) of the BGA component 10—totransversely deflect in the plane of the layer of resilient conductivematerial 130 (as shown by arrows 265 a, 265 b). A notch 266 locatedintermediate of the semicircular arms 263 a, 263 b may facilitatedeflection thereof, respectively. Further, the hoop-shaped spring 262may also deflect downwardly into the via 126 in a manner similar to thecantilevered spring 162.

[0057] Thus, the forces exerted by the semicircular arms 263 a, 263 b aseach deflects transversely outward (in directions 265 a, 265 b,respectively) upon engagement with a conductive ball 41—in conjunctionwith, optionally, deflection of the semicircular arms 263 a, 263 bdownwardly into the via 126—form physical and electrical contact betweenthe hoop-shaped spring 262 and the conductive ball 41. In addition, theshape of the hoop-shaped spring 262 itself (i.e., the hollow centerportion 268) may facilitate alignment between the hoop-shaped spring 262and the conductive ball 41. Further, impingement of the semicirculararms 263 a, 263 b against the exterior surface of the conductive ball 41in conjunction with relative motion therebetween may result in thescraping of oxides and other contaminants from the exterior surface ofthe conductive ball 41. To enhance the removal of oxides andcontaminants from the exterior surface of the conductive ball 41, thehoop-shaped spring 262 may include a plurality of grooves 191 and ridges192 (see FIG. 6), a plurality of barbs or protrusions 193 (see FIG. 8),and/or a roughened surface portion 194 (see FIG. 9) formed on itsexterior surface or a portion thereof.

[0058] The hoop-shaped spring 262 may also be used in conjunction with avia 126 that opens only to the upper surface 122 of the substrate 120(see FIG. 8). Also, at least a portion of the hoop-shaped spring 262 maybe preformed with a permanent upward deflection, enabling thehoop-shaped spring 262 to be positioned directly over the upper surface122 of the substrate 120 with no via subjacent thereto (see FIG. 9). Apreformed, hoop-shaped spring 262 having a permanent upward deflectionmay increase the deflection (downward toward the upper surface 122 ofthe substrate 120) of the hoop-shaped spring 262 upon engagement with aconductive ball 41, thereby increasing the corresponding biasing forcesexerted on the conductive ball 41 and enhancing electrical contacttherewith.

[0059] In another embodiment of the present invention, a spring-biasedelectrical contact 160 comprises a spiral-shaped spring 362, as shown inFIGS. 12 and 13. The spiral-shaped spring 362 is formed in the resilientconductive layer 130 within an aperture 136, and the spiral-shapedspring 362 extends from a conductive trace 132 and over a via 126 formedin the substrate 120. The spiral-shaped spring 362 includes an uppersurface 364 for making physical and electrical contact with a conductiveball 41 (shown in dashed line in FIGS. 12 and 13) of the BGA package 10.Upon engagement with a conductive ball 41 of the BGA package 10, atleast a portion of the spiral-shaped spring 362 will deflect downwardlyinto the via 126, thereby exerting a biasing force against theconductive ball 41 and establishing physical and electrical contacttherewith. Also, as shown in FIG. 13, during engagement with theconductive ball 41 and deflection downwardly into the via 126, thespiral-shaped spring 362 may be configured to form a cup or recess 366for receiving the conductive ball 41 and aligning the conductive ball 41relative to the spiral-shaped spring 362.

[0060] To facilitate the removal of oxides and contaminants from theexterior surface of the conductive ball 41, the spiral-shaped spring 362may includes a plurality of grooves 191 and ridges 192 (see FIG. 6), aplurality of barbs or protrusions 193 (see FIG. 8), and/or a roughenedsurface portion 194 (see FIG. 9) formed on its upper surface 364 or aportion thereof. Also, the spiral-shaped spring 362 may be used inconjunction with a via 126 that opens only to the upper surface 122 ofthe substrate 120 (see FIG. 8). Further, at least a portion of thespiral-shaped spring 362 may be permanently deflected upwardly toincrease the deflection of the spiral-shaped spring 362 upon engagementwith a conductive ball 41, thereby increasing the biasing forces exertedagainst the conductive ball 41 and enhancing electrical contacttherewith. For a preformed spiral-shaped spring 362 having a permanentupward deflection, the spiral-shaped spring 362 may be positioneddirectly over the upper surface 122 of the substrate 120 with no viasubjacent thereto (see FIG. 9).

[0061] In a further embodiment of the present invention, as shown inFIGS. 14 and 15, a spring-biased electrical contact 160 may comprise arosette spring 462 having a plurality of cantilevered pedals. Forexample, as shown in FIG. 14, the rosette spring 462 may include fourcantilevered pedals 464 a, 464 b, 464 c, 464 d or any other suitablenumber of cantilevered pedals. Each of the cantilevered pedals 464 a-d,respectively, includes a portion overlying and adhered to the uppersurface 122 of the substrate 120 and another portion extending over avia 126 extending through the substrate 120. Each of the cantileveredpedals 464 a-d also includes an upper surface 465 a-d, respectively, formaking physical and electrical contact with a conductive ball 41 (shownin dashed line in FIGS. 14 and 15) of the BGA package 10. Further, thecantilevered pedals 464 a-d each terminate at a central opening 466, thecentral opening 466 serving to facilitate alignment a conductive ball 41relative to the rosette spring 462.

[0062] The cantilevered pedals 464 a-d, or a portion thereof, may bepermanently upwardly deflected, as shown in FIG. 15, to increase thedeflection of the cantilevered pedals 464 a-d, respectively, uponengagement with a conductive ball 41, thereby increasing the biasingforce exerted against the conductive ball 41 and enhancing electricalcontact therewith. Such a rosette spring 462 preformed with permanentlyupwardly deflected pedals 464 a-d may be positioned directly over theupper surface 122 of the substrate 120 with no underlying via (see FIG.9). Also, the rosette spring 462 may be used in conjunction with a via126 opening onto only the upper surface 122 of the substrate 120 (seeFIG. 8). In a further alternative embodiment, the pedals 464 a-d of therosette spring 462 may be permanently downwardly deflected into the via126. In this embodiment, the upper surfaces 465 a-d of the cantileveredpedals 464 a-d, respectively, may function to guide a conductive ball 41toward the central opening 466, thereby facilitating alignment betweenthe conductive ball 41 and the rosette spring 462.

[0063] Referring again to FIGS. 14 and 15, a cavity 133 formed in thelayer of resilient conductive material 130 separates and electricallyisolates the rosette spring 462 (as well as the associated conductivetrace 132) from the remainder of the layer of resilient conductivematerial 130. Further, to facilitate the removal of oxides andcontaminants from the exterior surface of a conductive ball 41, therosette spring 462 may include cantilevered pedals 464 a-d having aplurality of grooves 191 and ridges 192 (see FIG. 6), a plurality ofbarbs or protrusions 193 (see FIG. 8), and/or a portion of roughenedsurface 194 (see FIG. 9) formed on their respective upper surfaces 465a-d, or a portion thereof.

[0064] Referring to FIG. 16, an MCM 500 incorporating a carriersubstrate 520 and a plurality of spring-biased electrical contacts 560according to the present invention is shown. One or more BGA packages 10a are mounted to an upper surface 522 of the carrier substrate 520 andone or more BGA packages 10 b may be mounted to an opposing lowersurface 524 of the carrier substrate 520 (again, the labels “upper” and“lower” being arbitrary). Although IC devices are shown mounted to bothsurfaces 522, 524 of the carrier substrate 520, those of ordinary skillin the art will understand that the MCM 500 may have IC devices mountedto only one of its carrier substrate surfaces 522, 524. Further, inaddition to the BGA packages 10 a, 10 b mounted on the MCM carriersubstrate 520, other electrical components and/or devices (not shown inFIG. 16) may also be mounted to the carrier substrate 520, as notedabove.

[0065] Each of the upper and lower surfaces 522, 524 of the carriersubstrate 520 includes a layer of resilient conductive material 530 a,530 b, respectively, formed thereon. A plurality of conductive traces532 a are formed in the resilient conductive material layer 530 a on thesubstrate upper surface 522, and a plurality of conductive traces 532 bare formed in the layer of resilient conductive material 530 b on thesubstrate lower surface 524. At least some of the conductive traces 532a on the upper surface 522 of the substrate 520 terminate atspring-biased electrical contacts 560 a. The spring-biased electricalcontacts 560 a on the upper surface 522 are arranged in one or moretwo-dimensional arrays corresponding to the pinout of the BGA package orpackages 10 a to be mounted thereon. Similarly, at least some of theconductive traces 532 b on the lower surface 524 of the carriersubstrate 520 terminate at spring-biased electrical contacts 560 b. Thespring-biased electrical contacts 560 b on the lower surface 524 arearranged in one or more two-dimensional arrays corresponding to thepinout of the BGA package or packages 10 b to be mounted thereon.

[0066] The spring-biased electrical contacts 560 a, 560 b may comprisecantilevered springs 162 (see FIGS. 3 through 9), transverselydeflecting hoop-shaped springs 262 (see FIGS. 10 and 11), spiral-shapedsprings 362 (see FIGS. 12 and 13), or rosette springs 462 (see FIGS. 14and 15), or any suitable configuration or combination thereof. Also, thespring-biased electrical contacts 560 a may each be preformed with apermanent deflection towards or away from the upper surface 522 of thesubstrate 520, and each spring-biased electrical contact 560 a mayextend over a via 526 opening to at least the upper surface 522 or,alternatively, be positioned directly over the upper surface 522 with nosubjacent via. Similarly, the spring-biased electrical contacts 560 bmay each be preformed with a permanent deflection towards or away fromthe lower surface 524 of the carrier substrate 520, and eachspring-biased electrical contact 560 b may extend over a via 526 openingto at least the lower surface 524 or, alternatively, be positioneddirectly over the lower surface 524 with no underlying via.

[0067] To electrically connect the BGA packages 10 a, 10 b to thecarrier substrate 520 of the MCM 500, each of the conductive balls 41 a,41 b on the BGA packages 10 a, 10 b, respectively, is engaged with amating spring-biased electrical contact 560 a, 560 b disposed on the MCMcarrier substrate 520. Clamping elements 90 a, 90 b—which are shown inFIG. 16 as stab-in-place clips 95—secure the BGA packages 10 a, 10 b,respectively, against the carrier substrate 520 to bias the conductiveballs 41 a, 41 b against their mating spring-biased electrical contact560 a, 560 b. The spring-biased electrical contacts 560 a, 560 b, eachof which exhibits a deflection as a result of engagement with aconductive ball 41 a, 41 b, exert a biasing force against their matingconductive ball 41 a, 41 b and form physical and electrical contacttherewith. To facilitate the removal of oxides and contaminants from theexterior surface of a conductive ball 41 a, 41 b and to enhanceelectrical contact therewith, the spring-biased electrical contacts 560a, 560 b may each include a plurality of grooves 191 and ridges 192 (seeFIG. 6), a plurality of barbs or protrusions 193 (see FIG. 8), and/or aroughened surface portion 194 (see FIG. 9) formed on a surface or aportion of a surface thereof.

[0068] Although the spring-biased electrical contacts 160, 162, 262,362, 462, 560 a, 560 b according to the present invention have beendescribed herein in the context of establishing electrical connectionswith the conductive balls 41 of a conventional BGA package 10, it shouldbe understood by those of ordinary skill in the art that the presentinvention is not so limited. The spring-biased electrical contacts 160,162, 262, 362, 462, 560 a, 560 b may be used to electrically connect theleads of other types of IC packages to a substrate, such as thesubstrate 120 of substrate assembly 100 or the carrier substrate 520 ofMCM 500. For example, any of the spring-biased electrical contacts 160,162, 262, 362, 462, 560 a, 560 b incorporating any of the featuresdescribed herein may be used to electrically connect the lead elementsor lead fingers of an SOJ package or the lead elements or lead fingersof a TSOP to a substrate. Also, those of ordinary skill in the art willappreciate that the various features described herein—i.e., preformeddeflections, via 126 extending through substrate, via 126 opening onlyto one surface of substrate, no subjacent via, and contact elements 191,192, 193, 194—may be incorporated in any suitable combination with anyof the spring-biased electrical contacts 160, 162, 262, 362, 462, 560 a,560 b described herein.

[0069] The present invention also encompasses methods of manufacturing asubstrate assembly 100, 500—including substrates 120, 520 andspring-biased electrical contacts 160, 162, 262, 362, 462, 560 a, 560 b,as described above—according to the present invention. Referring to theflow chart of FIG. 17, from which the methods of the invention may bebetter understood, various embodiments of a sequence of acts or steps,generally denoted as 600, comprising various methods according to thepresent invention are shown. One embodiment of such a method begins withthe act 610 of providing a substrate. The substrate may comprise an MCMcarrier substrate, a burn-in board, or other test board, and thesubstrate may comprise any suitable material or combination ofmaterials, including PCB materials, plastics, resins, composites,glasses, ceramics, and other oxide materials, as noted above. Thesubstrate generally includes a first surface and an opposing, secondsurface.

[0070] Once a substrate has been provided, the act 620 of forming alayer of resilient conductive material on a surface of the substrate isperformed. A layer of resilient conductive material may be applied toeither one or both of the first and second surfaces of the substrate,and the layer of resilient conductive material may cover only a portionof the first surface and/or a portion of the second surface. Theresilient conductive material may be any suitable material exhibitingsufficient electrical conductivity and suitable mechanical propertiesfor the formation of spring-biased electrical contacts. A berylliumcopper material is believed suitable for this purpose. It should benoted that the desired spring characteristics, as well as othermechanical properties, may be achieved by a heat treatment or othersuitable processing, as will be described in greater detail below. Anysuitable deposition process such as CVD or sputtering may be used toform the layer of resilient conductive material on a surface of thesubstrate, as noted above. Further, the layer of resilient conductivematerial may be a laminate that is secured or laminated onto a surfaceof the substrate using an adhesive and/or a thermocompression bondingprocess, also as noted above.

[0071] After the application of a layer of resilient conductive materialto one or more of the surfaces of the substrate, the act 630 of formingconductive traces, spring-biased electrical contacts, and apertures inthe resilient conductive material layer is performed. An etchingprocess, laser ablation process, or any other suitable material removalprocess, as noted above, may be used to form the conductive traces,spring-biased electrical contacts, and apertures in the resilientconductive material layer. Also, a stamping process may be used to formthe shapes of the spring-biased electrical contacts. The cavitiesdefining the conductive traces, as well as the apertures surrounding thespring-biased electrical contacts, extend at least to the surface of thesubstrate and, optionally, may extend a depth into the substrate. Thespring-biased electrical contacts may be configured in one or moretwo-dimensional arrays, each two-dimensional array corresponding to thepinout of an IC device to be mounted on the substrate. Also, thespring-biased electrical contacts may comprise any of the spring-biasedelectrical contacts described herein or a combination thereof.

[0072] Subsequent to the formation of conductive traces, spring-biasedelectrical contacts, and apertures in the layer of resilient conductivematerial on one or both of the opposing surfaces of the substrate, thesubstrate assembly is then subjected to a heat treatment process 640.Heat treating the substrate assembly after formation enables therealization of desired mechanical properties for the spring-biasedelectrical contacts while, at the same time, providing for suitablemechanical properties in the resilient conductive material layer duringformation of the conductive traces, spring-biased electrical contacts,and apertures. For example, it may be desirable for the resilientconductive material layer to exhibit good ductility during the formationof the conductive traces and spring-biased electrical contacts; however,high ductility is generally undesirable for a spring, which shouldretain its shape. In contrast, it may be desirable for the spring-biasedelectrical contacts to exhibit high strength and sufficient elasticity,but high strength and elasticity may impede formation of thespring-biased electrical contacts, as well as the formation of otherfeatures in the resilient conductive material layer. In addition, a heattreatment may effect stress relief within the resilient conductivematerial layer, which may be especially beneficial if the spring-biasedelectrical contacts include preformed deflections.

[0073] In lieu of heat treatment, other known metallurgical treatingprocesses may be employed to provide high strength and sufficientelasticity to the spring-biased electrical contacts. For example and notby way of limitation, air hardening, gas hardening or age hardening maybe employed. Treatment of beryllium copper to enhance and modify certainphysical characteristics thereof is known in the art, and BurchEngineered Materials, Inc. (formerly Brush Wellman) of Cleveland, Ohiooffers technical assistance in this area. As used herein, the term“treatment” encompasses heat treating as well as other processes formodifying physical characteristics of the resilient conductive materialor selected portions thereof.

[0074] Thus, the method of fabricating the substrate assembly andsubsequently heat treating the substrate assembly provides for desiredmechanical properties of the resilient conductive material duringformation of the spring-biased electrical contacts and other featuresand also enables the realization of desired mechanical properties forthe completed substrate assembly, such as desired spring characteristicsfor the spring-biased electrical contacts, as noted above. Essentially,the resilient conductive material layer or laminate applied to a surfaceof the substrate includes all necessary circuitry and electricalcontacts for establishing electrical communication with any IC devicesto be secured to the substrate, which circuitry and electrical contactsare formed in situ on the substrate. The above-described method standsin contrast to known methods of manufacturing spring-biased contacts forsubstrates and IC sockets, wherein the spring contacts are generallyformed, subjected to a heat treatment, and then subsequently secured orinserted into the substrate or IC socket.

[0075] In an alternative embodiment of a method of manufacturing asubstrate assembly according to the invention, the method proceeds asdescribed above with respect to FIG. 17; however, the method furtherincludes the act 624 of forming vias in the substrate. The apertures mayopen to only one surface or both surfaces of the substrate, and each ofthe vias is generally disposed subjacent a spring-biased electricalcontact and is substantially concentric with the corresponding apertureformed in the layer of resilient conductive material, as noted above.The vias may be formed using any suitable process, including drilling,cutting, etching, laser cutting/ablation, water jet cutting/ablation,punching, or stamping. Also, it should be noted that it may be desirableto form vias subjacent a portion of the spring-biased electricalcontacts on a surface of the substrate, while another portion of thespring-biased electrical contacts on that surface have no associatedvias.

[0076] In another alternative embodiment of a method of manufacturing asubstrate assembly according to the invention, the method proceedsaccording to either of the embodiments described above; however, themethod further includes the act 634 of preforming the spring-biasedelectrical contacts, or a portion thereof. The spring-biased electricalcontacts may be preformed to include a permanent deflection eithertoward or away from the underlying surface of the substrate, as notedabove. Such deflection may be imparted to a spring-biased electricalcontact by inserting a tool into the associated via and pulling orpushing on the spring-biased electrical contact until the contactexhibits the desired deflection.

[0077] In a further alternative embodiment of a method of manufacturinga substrate assembly according to the invention, the method proceedsaccording to any of the embodiments described above; however, the methodfurther includes the act 636 of forming contact elements on thespring-biased electrical contacts or a portion thereof. The contactelements may comprise a plurality of alternating grooves or ridges, aplurality of barbs or protrusions, or a portion of roughened surface, asdescribed above, or any other suitable contact elements known in theart.

[0078] If optional overlying dielectric layer 121 is employed in thesubstrate assembly of the present invention, it is desirably formed orapplied over the layer of resilient conductive material after theformation of all traces, spring-biased electrical contacts and contactelements as previously described. If applied as a film over the layer ofresilient conductive material, the overlying dielectric layer 121 mayhave preformed apertures 123 therein aligned with the spring-biasedelectrical contacts. If formed over the layer of resilient conductivematerial, the overlying dielectric material may be applied, for example,as a liquid, gel or paste and patterned and etched as known in the artto form apertures 123. Depending upon the dielectric material andetchant(s) chosen, apertures 123 may be formed either in substantiallycylindrical shapes with an aniosotropic etch or in frustoconical shapesusing a substantially isotropic etch.

[0079] Substrates and spring-biased electrical contacts according to thepresent invention, as well as substrate assemblies incorporating thesame, having been herein described, those of ordinary skill in the artwill appreciate the many advantages of the present invention. One ormore arrays of spring-biased electrical contacts and associatedcircuitry may be formed directly in a layer of resilient conductivematerial in situ on a surface of a substrate to form a substrateassembly. The spring-biased electrical contacts provide for thenonpermanent and direct attachment of IC devices to the substrateassembly, the spring-biased electrical contacts also compensating fornonplanarities in the substrate and IC devices. Fabrication of asubstrate assembly according to the invention is achieved using optimummechanical properties for formation (e.g., ductility), while theresulting substrate assembly exhibits optimum mechanical properties forperformance (e.g., spring characteristics, high strength, elasticity,stress relief). Further, the methods of the present invention andresulting devices enable the direct and nonpermanent attachment of ICdevices to a substrate on a production scale without the use ofexpensive IC sockets. In addition, while the present invention has beendescribed in terms of nonpermanent attachment of IC devices to asubstrate, those of ordinary skill in the art will understand andappreciate that long term attachment, including what might be termed“permanent” attachment of IC devices to a substrate may be effectedusing the present invention. Such permanent, yet removable attachmentcapability may be particularly desirable when repair or replacement ofan IC device in long term service may be foreseen or contemplated.

[0080] The foregoing detailed description and accompanying drawings areonly illustrative and not restrictive. They have been provided primarilyfor a clear and comprehensive understanding of the present invention andno unnecessary limitations are to be understood therefrom. Numerousadditions, deletions, and modifications to the embodiments describedherein, as well as alternative arrangements, may be devised by thoseskilled in the art without departing from the spirt of the presentinvention and the scope of the appended claims.

What is claimed is:
 1. A substrate assembly, comprising: a substrate; alayer of resilient conductive material disposed proximate a surface ofsaid substrate, said layer of resilient conductive material defining aplurality of electrically isolated spring-biased electrical contacts,each electrically isolated spring-biased electrical contact having anelectrically isolated conductive trace extending therefrom and furtherincluding a surface configured for biasing against and electricallycontacting a lead element of an integrated circuit device.
 2. Thesubstrate assembly of claim 1, further comprising a plurality of viasdisposed in said substrate, each via of said plurality of vias openingonto at least said surface of said substrate and underlying one of saidplurality of electrically isolated spring-biased electrical contacts. 3.A substrate assembly, comprising: a substrate; a laminate sheet ofresilient conductive material bonded said substrate proximate a surfacethereof, said laminate sheet of resilient conductive material defining aplurality of electrically isolated spring-biased electrical contacts,each electrically isolated spring-biased electrical contact having anelectrically isolated conductive trace extending therefrom and furtherincluding a surface configured for biasing against and electricallycontacting a lead element of an integrated circuit device.
 4. Thesubstrate assembly of claim 3, further comprising a plurality of viasdisposed in said substrate, each via of said plurality of vias openingonto at least said surface of said substrate and underlying one of saidplurality of electrically isolated spring-biased electrical contacts. 5.A substrate assembly, comprising: a substrate having a first surface andan opposing second surface; a layer of resilient conductive materialproximate at least a portion of at least one of said first and secondsurfaces of said substrate; at least one spring-biased electricalcontact formed in said layer of resilient conductive material andelectrically isolated from said layer of resilient conductive materialby an aperture formed in said layer of resilient conductive material,said at least one spring-biased electrical contact including a surfaceconfigured for biasing against and electrically contacting a leadelement extending from an integrated circuit device; and at least oneconductive trace formed in said layer of resilient conductive materialand electrically isolated from said layer of resilient conductivematerial by at least one cavity, said at least one conductive traceterminating at said at least one spring-biased electrical contact. 6.The substrate assembly of claim 5, further comprising at least one viaextending through said substrate and disposed at a location aligned withsaid at least one spring-biased electrical contact.
 7. The substrateassembly of claim 6, wherein said at least one via opens only onto saidat least one of said first and second surfaces of said substrate.
 8. Thesubstrate assembly of claim 5, wherein said at least one spring-biasedelectrical contact comprises a cantilevered spring, a transverselydeflecting hoop-shaped spring, a spiral-shaped spring, or a rosettespring.
 9. The substrate assembly of claim 5, wherein said at least onespring-biased electrical contact is configured to at least partiallyalign said lead element extending from said integrated circuit devicerelative to said at least one spring-biased electrical contact.
 10. Thesubstrate assembly of claim 5, wherein said at least one spring-biasedelectrical contact further includes a permanent deflection.
 11. Thesubstrate assembly of claim 5, wherein said layer of resilientconductive material comprises a laminate bonded to said at least one ofsaid first and second surfaces of said substrate.
 12. The substrateassembly of claim 5, wherein said layer of resilient conductive materialcomprises a layer of material deposited on said at least one of saidfirst and second surfaces of said substrate using a deposition process.13. The substrate assembly of claim 5, wherein said at least onespring-biased electrical contact further includes at least one contactelement disposed on said surface and configured to remove or puncturethrough a layer of contaminants formed on an exterior surface of a leadelement extending from an integrated circuit device.
 14. The substrateassembly of claim 13, wherein said at least one contact elementcomprises a plurality of alternating grooves and ridges, a plurality ofprotrusions, or a roughened surface.
 15. An electrical component,comprising: a substrate having a first surface and an opposing secondsurface; a layer of resilient conductive material disposed proximate atleast a portion of said first surface of said substrate; a plurality ofspring-biased electrical contacts formed in said layer of resilientconductive material, each spring-biased electrical contact of saidplurality of spring-biased electrical contacts electrically isolatedfrom said layer of resilient conductive material by an aperture formedin said layer of resilient conductive material; a plurality ofconductive traces formed in said layer of resilient conductive material,at least a portion of said plurality of conductive traces eachterminating at one spring-biased electrical contact of said plurality ofspring-biased electrical contacts, each conductive trace of saidplurality of conductive traces electrically isolated from said layer ofresilient conductive material and all other conductive traces of saidplurality of conductive traces by at least one cavity; and at least oneintegrated circuit device disposed on said first surface of saidsubstrate, said plurality of spring-biased electrical contacts on saidfirst surface of said substrate arranged in at least one arraycorresponding to a footprint of a plurality of lead elements extendingfrom said at least one integrated circuit device, each lead element ofsaid plurality of lead elements of said at least one integrated circuitdevice biased against and electrically contacting one spring-biasedelectrical contact of said plurality of spring-biased electricalcontacts.
 16. The electrical component of claim 15, further comprising aclamping element securing said at least one integrated circuit device tosaid first surface of said substrate and biasing said plurality of leadelements extending therefrom against said at least one array ofspring-biased electrical contacts.
 17. The electrical component of claim15, wherein at least one spring-biased electrical contact of saidplurality of spring-biased electrical contacts includes a permanentdeflection.
 18. The electrical component of claim 17, wherein said atleast one spring-biased electrical contact is permanently deflected awayfrom said first surface of said substrate.
 19. The electrical componentof claim 15, further comprising a plurality of vias disposed in saidsubstrate, each via of said plurality of vias positioned at a locationunderlying one spring-biased electrical contact of said plurality ofspring-biased electrical contacts.
 20. The electrical component of claim19, wherein at least one spring-biased electrical contact of saidplurality of spring-biased electrical contacts is permanently deflectedtowards said first surface of said substrate and said via underlyingsaid at least one spring-biased electrical contact.
 21. The electricalcomponent of claim 20, wherein a surface of said at least onespring-biased electrical contact and a wall of said underlying viasubstantially traps a lead element of said plurality of lead elements ofsaid at least one integrated circuit device therebetween.
 22. Theelectrical component of claim 15, wherein said each spring-biasedelectrical contact comprises a cantilevered spring, a transverselydeflecting hoop-shaped spring, a spiral-shaped spring, or a rosettespring.
 23. The electrical component of claim 15, wherein said eachspring-biased electrical contact is configured to at least partiallyalign a mating lead element of said plurality of lead elements of saidat least one integrated circuit device relative thereto.
 24. Theelectrical component of claim 15, wherein said each spring-biasedelectrical contact includes at least one contact element configured toremove or puncture through a layer of contaminants formed on a surfaceof a mating lead element of said plurality of lead elements of said atleast one integrated circuit device.
 25. The electrical component ofclaim 24, wherein said at least one contact element comprises aplurality of alternating grooves and ridges, at least one protrusion, ora roughened surface.
 26. The electrical component of claim 15, furthercomprising: a second layer of resilient conductive material disposedover at least a portion of said second surface of said substrate; asecond plurality of spring-biased electrical contacts formed in saidsecond layer of resilient conductive material, each spring-biasedelectrical contact of said second plurality of spring-biased electricalcontacts electrically isolated from said second layer of resilientconductive material by an aperture formed in said second layer ofresilient conductive material; a second plurality of conductive tracesformed in said second layer of resilient conductive material, at least aportion of said second plurality of conductive traces each terminatingat one spring-biased electrical contact of said second plurality ofspring-biased electrical contacts, each conductive trace of said secondplurality of conductive traces electrically isolated from said secondlayer of resilient conductive material and all other conductive tracesof said second plurality of conductive traces by at least one cavity;and at least other integrated circuit device disposed on said secondsurface of said substrate, said second plurality of spring-biasedelectrical contacts on said second surface of said substrate arranged inat least one array corresponding to a footprint of a plurality of leadelements extending from said at least one other integrated circuitdevice, each lead element of said plurality of lead elements of said atleast one other integrated circuit device biased against andelectrically contacting one spring-biased electrical contact of saidsecond plurality of spring-biased electrical contacts.
 27. A method offabricating a substrate assembly, comprising: providing a substratehaving a first surface and an opposing second surface; forming a layerof resilient conductive material on at least a portion of at least oneof said first and second surfaces of said substrate; forming at leastone electrically isolated spring-biased electrical contact in said layerof resilient conductive material; forming at least one electricallyisolated conductive trace in said layer of resilient conductivematerial, said at least one electrically isolated conductive tracehaving an end terminating at said at least electrically isolatedspring-biased electrical contact; and treating said layer of resilientconductive material after said forming said at least one electricallyisolated spring-biased electrical contact to achieve at least onedesired physical characteristic of said layer of resilient conductivematerial.
 28. The method of claim 27, wherein said forming a layer ofresilient conductive material on at least a portion of at least one ofsaid first and second surface of said substrate comprises: providing alaminate sheet of said resilient conductive material; and bonding saidlaminate sheet to said at least one of said first and second surfaces ofsaid substrate.
 29. The method of claim 28, wherein said bonding saidlaminate sheet to said at least one of said first and second surfaces ofsaid substrate comprises adhering said laminate sheet to said at leastone of said first and second surfaces of said substrate using anadhesive or bonding said laminate sheet to said at least one of saidfirst and second surfaces of said substrate using a thermocompressionbonding process.
 30. The method of claim 27, wherein said forming alayer of resilient conductive material on at least a portion of at leastone of said first and second surfaces of said substrate comprisesforming said layer of resilient conductive material on said at least oneof said first and second surfaces of said substrate using a depositionprocess.
 31. The method of claim 30, wherein said deposition processcomprises chemical vapor deposition or sputtering.
 32. The method ofclaim 27, further comprising forming at least one via in said substrate,said at least one via underlying said at least one electrically isolatedspring-biased electrical contact.
 33. The method of claim 32, whereinsaid forming at least one via in said substrate further comprisesforming a via opening only to said at least one of said first and secondsurfaces of said substrate.
 34. The method of claim 27, furthercomprising preforming said at least one electrically isolatedspring-biased electrical contact to include a permanent deflection. 35.The method of claim 27, further comprising forming at least one contactelement on a surface of said at least one electrically isolatedspring-biased electrical contact.
 36. The method of claim 35, whereinsaid forming at least one contact element further comprises forming aplurality of alternating grooves and ridges, forming at least oneprotrusion, or forming a roughened surface.
 37. The method of claim 36,wherein forming a plurality of alternating grooves and ridges, formingat least one protrusion or forming a roughened surface is effected byetching.
 38. The method of claim 27, wherein said forming at least oneelectrically isolated spring-biased electrical contact in said layer ofresilient conductive material comprises forming a cantilevered spring,forming a transversely deflecting hoop-shaped spring, forming aspiral-shaped spring, or forming a rosette spring.
 39. The method ofclaim 27, wherein at least one of forming at least one electricallyisolated spring-biased electrical contact in said layer of resilientconductive material and forming at least one electrically isolatedconductive trace in said layer of resilient conductive material iseffected by etching said layer of resilient conductive material.
 40. Amethod of fabricating a substrate assembly, comprising: providing asubstrate having a first surface and an opposing second surface; forminga layer of resilient conductive material on at least a portion of atleast one of said first and second surfaces of said substrate, saidresilient conductive material exhibiting at least one first physicalcharacteristic; forming at least one electrically isolated spring-biasedelectrical contact in said layer of resilient conductive material;forming at least one electrically isolated conductive trace in saidlayer of resilient conductive material, said at least one electricallyisolated conductive trace having an end terminating at said at least oneelectrically isolated spring-biased electrical contact; and treatingsaid layer of resilient conductive material to achieve at least onesecond physical characteristic of said resilient conductive material.41. The method of claim 40, wherein said at least one first physicalcharacteristic is selected to optimize properties of said layer ofresilient conductive material for said act of forming at least oneelectrically isolated spring-biased electrical contact therein.
 42. Themethod of claim 40, wherein said at least one second physicalcharacteristic is selected to optimize spring characteristics of said atleast one electrically isolated spring-biased electrical contact. 43.The method of claim 40, wherein at least one of forming at least oneelectrically isolated spring-biased electrical contact in said layer ofresilient conductive material and forming at least one electricallyisolated conductive trace in said layer of resilient conductive materialis effected by etching said layer of resilient conductive material. 44.The substrate assembly of claim 1, further including a dielectric layeroverlying said layer of resilient conductive material and havingapertures therethrough substantially aligned with said electricallyisolated spring-biased electrical contacts.
 45. The substrate assemblyof claim 44, wherein the dielectric layer is of sufficient thickness toencompass at least a portion of each lead element of an integratedcircuit device contacting an electrically isolated spring-biasedelectrical contact.
 46. The substrate assembly of claim 45, wherein saidapertures are of frustoconical configuration.
 47. The substrate assemblyof claim 3, further including a dielectric layer overlying said layer ofresilient conductive material and having apertures therethroughsubstantially aligned with said electrically isolated spring-biasedelectrical contacts.
 48. The substrate assembly of claim 47, wherein thedielectric layer is of sufficient thickness to encompass at least aportion of each lead element of an integrated circuit device contactingan electrically isolated spring-biased electrical contact.
 49. Thesubstrate assembly of claim 48, wherein said apertures are offrustoconical configuration.
 50. The substrate assembly of claim 5,further including a dielectric layer overlying said layer of resilientconductive material and having at least one aperture therethroughsubstantially aligned with said at least one electrically isolatedspring-biased electrical contact.
 51. The substrate assembly of claim50, wherein the dielectric layer is of sufficient thickness to encompassat least a portion of at least one lead element of an integrated circuitdevice contacting said at least one electrically isolated spring-biasedelectrical contact.
 52. The substrate assembly of claim 51, wherein saidat least one aperture is of frustoconical configuration.
 53. Theelectrical component of claim 15, further including a dielectric layeroverlying said layer of resilient conductive material and havingapertures therethrough substantially aligned with said electricallyisolated spring-biased electrical contacts.
 54. The substrate assemblyof claim 53, wherein the dielectric layer is of sufficient thickness toencompass at least a portion of each lead element of said at least oneintegrated circuit device contacting an electrically isolatedspring-biased electrical contact.
 55. The substrate assembly of claim54, wherein said apertures are of frustoconical configuration.
 56. Themethod of claim 27, further including disposing a dielectric layeroverlying said layer of resilient conductive material, said dielectriclayer being formed with at least one aperture therethrough substantiallyaligned with said at least one electrically isolated spring-biasedelectrical contact.
 57. The method of claim 56, further comprisingforming said dielectric layer to be of sufficient thickness to encompassat least a portion of each lead element of an integrated circuit devicecontacting said at least one electrically isolated spring-biasedelectrical contact.
 58. The method of claim 58, further includingforming said at least one aperture to be of frustoconical configuration.59. The method of claim 56, further including preforming said dielectriclayer with said at least one aperture prior to disposing said dielectriclayer over said layer of resilient conductive material.
 60. The methodof claim 56, further including forming said dielectric layer in placeover said layer of resilient conductive material and subsequentlyforming said at least one aperture therethrough.
 61. The method of claim40, further including disposing a dielectric layer over said layer ofresilient conductive material, said dielectric layer being formed withat least one aperture therethrough substantially aligned with said atleast one electrically isolated spring-biased electrical contact. 62.The method of claim 61, further comprising forming said dielectric layerto be of sufficient thickness to encompass at least a portion of eachlead element of an integrated circuit device contacting said at leastone electrically isolated spring-biased electrical contact.
 63. Themethod of claim 62, further including forming said at least one apertureto be of frustoconical configuration.
 64. The method of claim 61,further including preforming said dielectric layer with said at leastone aperture prior to disposing said dielectric layer over said layer ofresilient conductive material.
 65. The method of claim 61, furtherincluding forming said dielectric layer in place over said layer ofresilient conductive material and subsequently forming said at least oneaperture therethrough.